In the process of manufacturing ICs with LSI, VLSI and ULSI, patterned material layers like patterned photoresist layers, patterned barrier material layers containing or consisting of titanium nitride, tantalum or tantalum nitride, patterned multi-stack material layers containing or consisting of stacks e.g. of alternating polysilicon and silicon dioxide layers, and patterned dielectric material layers containing or consisting of silicon dioxide or low-k or ultra-low-k dielectric materials are produced by photolithographic techniques. Nowadays, such patterned material layers comprise structures of dimensions even below 20 nm with high aspect ratios.
Photolithography is a method in which a pattern on a mask is projected onto a substrate such as a semiconductor wafer. Semiconductor photolithography typically includes the step of applying a layer of a photoresist on a top surface of the semiconductor substrate and exposing the photoresist to actinic radiation, in particular UV radiation of a wavelength of, for example, 193 nm, through the mask. In order to extend the 193 nm photolithography to the 20 nm and the 15 nm technology node, immersion photolithography has been developed as a resolution enhancement technique. In this technique, the air gap between the final lens of the optical system and the photoresist surface is replaced by a liquid medium that has a refractive index greater than one, e.g., ultra pure water with a refractive index of 1.44 for the wavelength of 193 nm. However, in order to avoid leaching, water-uptake and pattern degradation, a barrier coating or a water resistant photoresist must be used. These measures however add to the complexity of the manufacturing process and are therefore disadvantageous.
Besides the 193 nm immersion lithography, other irradiation techniques using significant shorter wavelengths are considered to be solutions which fulfil the needs of further downscaling of the to be printed feature sizes of the 20 nm technology node and below. Besides electron beam (eBeam) exposure, the Extreme Ultraviolett (EUV) lithography with a wavelength of about 13.5 nm seems to be the most promising candidate to replace immersion lithography in the future. After the exposure, the subsequent process flow is quite similar for immersion eBeam and EUV lithography as described in the following paragraph.
A post-exposure bake (PEB) is often performed to allow the exposed photoresist polymers to cleave. The substrate including the cleaved polymer photoresist is then transferred to a developing chamber to remove the exposed photoresist, which is soluble in aqueous developer solutions. Typically, a developer solution such as tetramethylammonium hydroxide (TMAH) is applied to the resist surface in the form of a puddle to develop the exposed photoresist. A deionized water rinse is then applied to the substrate to remove the dissolved polymers of the photoresists. The substrate is then sent to a spin drying process. Thereafter, the substrate can be transferred to the next process step, which may include a hard bake process to remove any moisture from the photoresist surface.
Irrespective of the exposure techniques, the wet chemical processing of small patterns involves however a plurality of problems. As technologies advance and dimension requirements become stricter and stricter, photoresist patterns are required to include relatively thin and tall structures or features of photoresists, i.e., features having a high aspect ratio, on the substrate. These structures may suffer from bending and/or collapsing, in particular, during the spin dry process, due to excessive capillary forces of the deionized water remaining from the chemical rinse and spin dry processes and being disposed between adjacent photoresist features. The maximum stress a between small features caused by the capillary forces can be defined as follows:
  σ  =                              6          ·          γ          ·          cos                ⁢                                  ⁢        θ            D        ·                  (                  H          W                )            2      
wherein γ=surface tension of the fluid, θ=contact angle of the fluid on the feature material surface, D=distance between the features, H=height of the features, and W=width of the features. Consequently, the surface tension of the chemical rinse solutions must be significantly lowered.
Another solution for immersion lithography may include using a photoresist with modified polymers to make it more hydrophobic. However, this solution may decrease the wettability of the developing solution.
Another problem of the conventional photolithographic process is line edge roughness (LER) due to resist and optical resolution limits. LER includes horizontal and vertical deviations from the feature's ideal form. Especially as critical dimensions shrink, the LER becomes more problematic and may cause yield loss in the manufacturing process of IC devices.
Due to the shrinkage of the dimensions, the removal of particles in order to achieve a defect reduction becomes also a critical factor. This does not only apply to photoresist patterns but also to other patterned material layers which are generated during the manufacture of optical devices, micromachines and mechanical precision devices.
An additional problem of the conventional photolithographic process is the presence of watermark defects. Watermarks may form on the photoresist as the deionized water or rinse liquid cannot be spun off from the hydrophobic surface of the photoresist. The photoresist may be hydrophobic particularly in areas of isolated, or non-dense, patterning. The watermarks have a harmful effect on yield and IC device performance.
The American patent application US 2008/0280230 A1 discloses a chemical rinse solution containing an alcohol, in particular, isobutyl alcohol. Moreover, the chemical rinse solution may contain fluorosurfactants such as 3M Novec™ fluid HFE-711 PA, -7000, -7100, -7200, and 7500, 3M Fluorinert™ FC-72, -84, -77, -3255, -3283, -40, -43, -70, -4432, 4430, and -4434, or 3M Novec™ 4200 and 4300.
For instance, 3M Novec™ 4200 is a perfluoroalkyl sulfonamide, 3M Novec™ 4300 is a perfluoroalkyl sulfonate, HFE-7000 is heptafluoro-3-methoxypropane, HFE-7100 is nonafluoro-4-methoxybutane, HFE-7200 is 1-ethoxy-nonafluorobutane, HFE-7500 is 3-ethoxy-dodecafluoro-2-(trifluoromethyl)-hexane, and HFE-711 PA is an azeotrope of 1-methoxy-nonafluorobutane and isopropanol. The 3M Fluorinert™ series surfactants are customarily used as inert perfluorinated heat transfer media.
The American patent application US 2008/0299487 A1 teaches the use of the above mentioned fluorosurfactants as additives to developer and chemical rinse solutions as well as to the immersion photoresist material. Moreover, 3M L-18691, an aqueous solution of perfluoroalkyl sulfonimide, can also be used. Additionally, the use of the following fluorosurfactants is suggested:                Rf—SO3−M+, wherein Rf is a C1-C12 perfluoroalkyl group and M+ is a cation, a proton or an ammonium group;        Rf—SO2N−—R1M+, wherein Rf and M+ have the above-mentioned meaning and R1 is a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkylamine oxide group, an alkylcarboxylate group or an aminoalkyl group, the alkyl, hydroxyalkyl, alkylamine oxide, alkylcarboxylate and aminoalkyl groups having preferably 1-6 carbon atoms and the hydroxyalkyl having preferably the formula —(CH2)x—OH, wherein x=1-6; and        Rf-Q-R1SO3−M+, wherein Rf and M+ have the above-mentioned meaning and R1 is an alkylene of the formula —CnH2n(CHOH)oCmH2m-, wherein n and m are independently of each other 1-6 and o is 0-1, and is optionally substituted by catenary oxygen or nitrogen group, Q is —O— or —SO2NR2—, wherein R2 is a hydrogen atom, or an alkyl, aryl, hydroxyalkyl, aminoalkyl, or a sulfonatoalkyl group having 1-6 carbon atoms, optionally containing one or more catenary oxygen or nitrogen heteroatoms; the hydroxyalkyl group may be of the formula —CpH2p—OH, wherein p is 1-6; the aminoalkyl group may be of the formula —CpH2p—NR3R4, wherein p is 1-6 and R3 and R4 are independently of each other hydrogen atoms or alkyl groups of 1-6 carbon atoms.        
The American patent applications US 2008/0280230 A and US 2008/0299487 A1 remain silent as to whether the chemical rinse solutions containing such an ionic fluorosurfactant can meet the ever increasing demands of the IC manufacturing industry, in particular with regard to pattern collapse in the 32 nm and sub-32 nm technology nodes.
The international patent applications WO 2008/003443 A1, WO 2008/003445 A1, WO 2008/003446 A2 and WO 2009/149807 A1 and the American patent application US 2009/0264525 A1 disclose inter alia cationic and anionic fluorosurfactants. These known fluorosurfactants find numerous applications, for example, in textile, paper, glass, building, coating, cleaner, cosmetic, herbicide, pesticide, fungicide, adhesive, metal, or mineral oil technologies as well as in special coatings for semiconductor photolithography (photoresist, top antireflective coatings, bottom antireflective coatings) [cf., for example WO 2008/003446 A2, page 14, line 29 to page 20, line 20]. The use of the fluorosurfactants for manufacturing ICs for nodes of 50 nm and lower, in particular for 32 nm nodes and lower, is not disclosed. Moreover, many of these prior art fluorosurfactants are not easily biodegradable and are therefore prone to bioaccumulation.